In the most common method currently in use for fastening the screen wiper arm on to the motor shaft, so that the latter can drive the wiper arm in rotation, the end portion of the motor shaft has a conical portion which is received in a complementary conical through hole associated therewith and formed in the drive head. This conical portion of the motor shaft is extended by a threaded terminal shank of the shaft, on to which a fastening nut is screwed. The radial thrust surface of the nut cooperates with a portion, in facing relationship with it, of the upper face of the drive head.
In one known arrangement, the axis of the conical through hole is perpendicular to the flat upper and lower faces of the drive head of the screen wiper arm, in such a way that, in the assembled condition, these two faces lie in planes which are at right angles to the axis of rotation of the motor shaft. This geometrical arrangement determines the general orientation of the screen wiper arm, of the screen wiper blade which is pivoted to the outer end of the wiper arm, and of the wiping strip which is carried by the wiper blade. This orientation is of course the orientation of these elements with respect to the structure of the vehicle, and therefore with respect to the surface which is to be swept, which may for example be the windshield of the vehicle.